Spatially resolved microchemical analysis of chromate‐conversion‐coated aluminum alloy AA2024‐T3

Abstract

The corrosion of aerospace aluminum alloys has been linked to the electrochemical behavior and chemical composition of constituent intermetallic compounds (IMCs). In this study, secondary ion mass spectrometry (SIMS), x-ray photoelectron spectroscopy (XPS), synchrotron infrared microspectrometry (SIRMS) and xray absorption near-edge structure spectroscopy (XANES) were used to characterize chromate conversion coatings (CCCs) formed on AA2024-T3 sheet and cast IMC analogs. The nascent surface film formed on IMC and matrix surfaces was characterized to reveal the influence of microstructure on CCC structure and composition. Copper-rich regions were found on the outermost CCC surface. Intermetallic compounds rich in Cu were found to be surface depleted of Cr and enriched in CN from the ferricyanide present in the CCC as an accelerator compound. By distinguishing particle morphology and chemistry, SIMS data demonstrated that heterogeneities in CCC composition were associated with IMCs.

Impact of the Fused Deposition (FDM) Printing Process on Polylactic Acid (PLA) Chemistry and Structure

“…In general, micro-chemical analysis combined with large area surface-sensitive spectroscopies and imaging, has proved to be essential for understanding the mechanisms controlling processing-performance relationships [19]. Figure 3 shows a side view of the source filament.…”

Electrochemical assessment of interfacial characteristics of intermetallic phases present in aluminium alloy 2024-T3

“…Since the reduction reaction of chromate is fast and exposure time is longer than that reported in Clark's work [60], the film may also involve the polymerization of Cr III on the monolayer [29], leading to a large thickness. It is also expected that the film thickness on each IMC would be different, which requires advanced surface techniques to characterise as studied in [30,31], and is not the focus of this work. The thickness of chromate film is roughly estimated using the measured capacitance in this work.…”

“…However, corrosion associated with the secondary phase particles is strongly supressed by the addition of chromate to the solution, which leads to the formation of a compact Cr III -Cr VI mixed hydroxide film [26][27][28]. The protective film is composed of chemisorbed Cr III oxides and adsorbed Cr VI oxides [29], and is chemically and topographically heterogeneous on the surface [30,31]. The thickness of the film on the AA2024 matrix and Al 20 Cu 2 Mn 3 particles are larger than that on Al 2 Cu and S-phase [31].…”

The Intersection of Design, Manufacturing, and Surface Engineering

“…The commercial aluminumÀcopper alloy AA2024-T3, primarily used in aircraft in the form of sheet and fuselage and plate for the lower wing, contains several alloying elements that lead to the formation of a complex, multiphase structure ( Figure 15.1). Cu, Mg, Mn, Si, and Fe are present in AA2024-T3 in appreciable amounts and form intermetallic compounds (IMCs) of composition Al 2 Cu, Al 2 CuMg, Al 2 Cu 2 Fe, Al 7 Cu 2 Fe, Al 12 Si(FeMn) 3 , Al 20 Cu 2 (MnFe) 3 , and Al 20 Cu 3 Mn 3 . These secondary phase precipitates and IMCs enhance the mechanical strength of the alloy.…”

“…However, it has been shown that the presence of IMCs strongly affects both the thickness and the surface morphology of CCC formed on AA2024-T3. 3 The application and corrosion-inhibiting mechanisms of these coatings will be discussed in some more detail in the following sections.…”